System and method for increased removal torque values for rationally engaging polymeric members

ABSTRACT

A torque retention apparatus and method for use with container-closure combinations including selection of retainer or other component materials such that variations in material properties of the materials and/or dimensional changes in the components over time contribute to substantially increased torque retention. Selection of container contents and the configuration of supplemental sealing and/or attachment features may further contribute to the substantial increase in torque retention. A fitment having an annular well and tubular wick retainer is interposed between the container and the closure.

FIELD OF INVENTION

The invention relates generally to methods of increasing torque retention in container-closure combinations including resilient polymeric retaining features.

BACKGROUND OF INVENTION

Containers are commonly fitted with a removable cap or other closure. Common container-closure combinations require application of a set torque to the closure during assembly, generating friction between complimentary retainers formed on the container and closure. For example, a common closure includes internal features such as threads or lugs for engaging external features such as complimentary threads formed on the container exterior. Additional closure and/or container features are commonly employed to form various seals when advanced into sealing engagement by rotational engagement of the threads. For example, an o-ring may be sealingly compressed between the closure and container by application of sufficient torque to the closure. Similarly, additionally container fitments such as, for example, pour spouts or wick holders, may be interposed between the container and closure.

In containers using resilient plastic threaded members, the plastic material may exhibit creep, relaxation, or cold flow due to the forces caused during application of the set torque during installation or by expansion of materials within the container. This creep or cold flow often causes a gradual loosening of the threaded connection. In addition, plastic materials typically have a low coefficient of friction, causing gradual movement and loosening referred to as “backoff slippage” of the threaded connection. It is a concern that excessive creep or backoff slippage may compromise a seal or even result in separation of a fitment or closure from a container.

Application of insufficient set torque during installation of the closure on the container may affect performance of sealing features during storage, shipping, and handling. Application of too much toque may result in stripping of the threads or may render the connection too tight for removal by hand. A concern with known systems employing resilient polymeric components is that plastic creep, material flexure, or backoff slippage may lead to a reduction in the sealing forces initially generated by the set torque. “Torque retention” or “torque reduction,” as used in the art, refer to relative degrees of variation between the set torque and the removal torque. In laboratory and quality control testing, the removal torque is often measured after an extended period at ambient temperatures or after a shortened period at high temperatures to simulate an expected shelf or storage life of the product. The elevated temperature accelerates the creep, material flexure, or backoff slippage of the plastic components.

Typically, set torques of two to four times the desired removal torque are used to allow for expected torque reduction. Thus, conventional configurations typically exhibit torque retention of fifty percent or less. For example, a plastic cap installed on a plastic container at a set torque of fifteen inch pounds may require a removal torque of only three to eight inch pounds.

In an attempt to enhance torque retention capabilities, earlier systems have proposed increased thread depth, supplemental thread elements, lugs, sealing rings, gaskets, and the like to provide additional friction between the threads. Such systems have achieved but modest increases in torque retention. Increased torque retention serves to reduce the amount of initial set torque required to obtain a desired removal torque. In some instances, it may even be desirable that the removal torque exceed the applied set torque, allowing for greatly reduced set torques during production.

Accordingly, it is desirable to provide an apparatus and method for significantly enhanced torque retention in container-closure configurations. In particular, there is a need for such configurations exhibiting retention of substantially more than half of an applied set torque. Indeed, there is further a need for configurations exhibiting removal torque values in excess of an applied set torque value.

SUMMARY OF INVENTION

In accordance with various exemplary embodiments of the present invention, selected combinations of polymeric materials, retainer configurations, and/or interaction of polymeric materials and container contents provide increased torque retention. Increased torque retention serves to improve closure and fitment seal performance and to reduce the amount of set torque required during installation.

Increased torque retention may be accomplished through selection of different polymeric materials for the container, closure, and/or fitment such that relative material properties of different components result in a significant increase in torque retention over an extended period. The invention may also provide friction in excess of that generated by the set torque during installation, resulting in a removal torque greater than the set torque.

Increased torque retention may also be accomplished by selection of the composition of the container contents to obtain a desired physical or chemical interaction with any of the materials of the container, fitment, and/or closure. Sealing features and/or friction generating features may also contribute to an increase in torque retention.

These and other aspects of the invention shall become more apparent when read in conjunction with the accompanying drawing figures and the attached detailed description of exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention are hereinafter described in the following detailed description of exemplary embodiments to be read in conjunction with the accompanying drawing figures, wherein like reference numerals are used to identify the same or similar parts in the similar views, and:

FIG. 1A is a plot showing torque retention of prior art systems;

FIG. 1B is a plot comparing torque retention according to an embodiment of the present invention with that of prior art systems;

FIG. 1C is a plot comparing torque retention according to another embodiment with that of prior art systems; and

FIG. 2 shows an exemplary threaded container, threaded closure and interposed wick fitment having multiple sealing features according to one embodiment of the present invention.

DETAILED DESCRIPTION

The following description is of exemplary embodiments of the invention only, and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description is intended to provide a convenient illustration for implementing various embodiments of the invention. As will become apparent, various changes may be made in the function and arrangement of the elements described in these embodiments without departing from the scope of the invention as set forth herein.

That said, in the context of the present invention, methods and apparatus described herein may find particular use in connection with air freshener refill combinations including a reservoir, fitment and cap. However, generally speaking, any container and closure combination or other rotationally engaging retainer combination may benefit from the present invention. Accordingly, the terms “container,” “refill,” “reservoir”, and “bottle” as used herein are intended to interchangeably refer to any first member having a retainer formed thereon. The terms “closure,” “cap,” and “fitment” may be used interchangeably herein and refer to any second member retained by a second retainer formed thereon or retained between the first member and a second member having a second retainer formed thereon.

Various embodiments of the present invention may be described herein in conjunction with specific devices or products and it should be appreciated that the scope of the present invention should not be considered limited to those specifically mentioned herein. As used herein “torque retention” refers to the relative degree of variation between the set torque and the removal torque for a given retainer combination. Increased torque retention may also be described in terms of the ratio of removal torque to an applied set torque, including ratios greater than one, i.e., where the removal torque exceeds the applied set torque.

In accordance with the present invention, a container is any reservoir, bottle, or repository and generally includes a hollow body with a neck portion defining an opening therein. A closure is any cap, cover, plug, or the like that is configured to cover or seal the opening in the container, for example by threadably engaging the neck of the container. A fitment is any plug, pour spout, or dispensing mechanism configured to engage the container opening in cooperation with a closure or independent of a closure. The container, closure and/or fitment engage or cooperate with one another by any number of cooperating retainer mechanisms such as mating threads, lugs, skirts, ledges, projections, flanges, and the like.

Container, closure, or fitment components may be injection molded, blow molded, or thermoformed of any suitable plastic material such as polypropylene, polyethylene, polyvinyl chloride, copolymers of the same, or other suitable polymers. Alternatively, components may be formed by machining of a bulk material or by any other known manufacturing process. Various embodiments are described herein in terms of polymers, but it should be understood that any other suitable material such as glass, metal, and the like may be used in accordance with the present invention. Increased torque retention may be accomplished in cooperating retainer mechanisms by any means that serves to increase the removal torque required to disengage a closure from a container after an extended period of engagement following application of a set torque.

Various torque retention properties of various embodiments of the present invention will now be described with reference to FIGS. 1A-1C. FIG. 1A illustrates an exemplary plot of torque retention exhibited by prior art configurations. As illustrated, a set torque is initially applied to the configuration of retainers. Over time, the torque required to disengage the retainers settles around or below one half of the initial set torque. As explained above, this torque reduction is due to material creep, cold flow, or other phenomenon.

FIG. 1B illustrates a plot of torque retention exhibited by an embodiment in accordance with the present invention versus that of the prior art shown in FIG. 1A. This figure illustrates the significant increase in torque retention of substantially greater than half of the applied set torque. Modest increases in torque retention provided by the prior art still yielded only retention values around or well below fifty percent. Thus, retention values of substantially more than fifty percent are a significant invention over the prior art.

FIG. 1C illustrates a plot of torque retention exhibited by another embodiment in accordance with the present invention versus that of the prior art shown in FIG. 1A. This figure illustrates a torque retention ratio greater than one, i.e., a removal torque in excess of the applied set torque.

In various embodiments, increased torque retention may be attributed to an increase in friction due to a selection of differing material properties, e.g., such as shrink rates, coefficients of thermal expansion, elastic moduli, tensile strengths, tensile moduli, flexural strengths, flexural moduli, compressive strengths, compressive moduli or other properties of the closure and the container. For example, increased shrink rates of the closure relative to the container may serve to increase friction between threaded interfaces as well as between interference sealing interfaces. Materials may be selected based on any material property or combination of material properties to achieve the desired degree of torque retention.

As shown in FIG. 2, an exemplary container-fitment-closure combination 2 includes a container 4 composed of polypropylene, a wick fitment 6 composed of a linear low density polyethylene, and a closure 8 composed of polypropylene. The polypropylene of container 4, polyethylene of fitment 6, and polypropylene of closure 8 are selected such that the relative material properties lead to a reduction in the loss of friction caused by creep or other phenomenon over time. For example, dimensional changes of one component relative to another may contribute to increased torque retention. Exemplary material properties of the various selected polymers include shrink rates, coefficients of thermal expansion, elastic moduli, tensile strengths, tensile moduli, flexural strengths, flexural moduli, compressive strengths, and compressive moduli.

In various other embodiments, increased torque retention may be accomplished through interaction of polymeric apparatus components and the contents of container 4. This interaction may be chemical or physical. For example, a chemical reaction between a scented oil held by container 4 and the polymer or other material of any of the apparatus components may increase the coefficient of friction of the material and thus the torque retention of the combination. Alternatively, the contents of container 4 may serve to facilitate a reaction between two materials composing two or more components of container-closure combination 2.

In accordance with various embodiments of the present invention, various combinations of multiple engaging features contribute to increased torque retention. With continued reference to FIG. 2, an air freshener refill container 4 holds scented oil that is drawn from container 4 by a wick (not shown). The wick is retained by a wick fitment 6 attached to the neck of refill container 4. Wick fitment 6 is a cylindrical disk having a central tubular formation 10 for positioning the wick and including an annular well 12, annular sealing groove 14, and a peripheral skirt 16 configured to engage a ledge 18 on the neck of container 4. Closure 8 includes screw threads 20 to engage mating threads 22 on container 4 and covers the wick and wick fitment 6 to prevent evaporation of the scented oil during storage. Closure 8 further includes an annular dam 24 on the underside of closure 8 for sealing against the side of fitment well 12 when assembled. An annular ridge 26 on the underside of closure 8 forms an additional seal with annular groove 14 in fitment 6.

Rotational engagement of threads 20 and 22 advances closure 8 onto container 4, compressing fitment 6 therebetween. Advancement of closure 8 onto container 4 also causes an interference fit between closure dam 24 and the sidewall of fitment well 12 as well as between closure sealing ridge 26 and fitment annular groove 14. Shrinkage of fitment well 12 in excess of that of closure dam 24 may serve to increase the sealing frictional interference between those features, resulting in an overall increase in the removal torque required to separate closure 8 from container 4. Additional gaskets, sealing rings, flanges, ribs, skirts, and the like may be used to provide additional sealing mechanisms between container 4 and closure 8, fitment 6 and container 4, and/or fitment 6 and closure 8. For example, multiple seals may be used to create a series of sealed zones such that failure of one seal does not result in leakage from the assembly as a whole.

Similarly, various attachment mechanisms such as, for example, attachment lugs, secondary thread sets, or thread variations (e.g., variations in thread depth, thread thickness, or other thread irregularities towards the end or beginning of engagement or along the full thread length), or any number of other features may serve to provide increased friction or other resistance to relative rotation of closure 8, container 4, and/or fitment 6. Thus, it is understood that any number or type of attachment or sealing mechanisms may be used in accordance with the present invention to achieve an increase in torque retention, including removal torques in excess of the applied set torque. It is further understood that any combination of any of the above described mechanisms (e.g., materials selection, interaction with contained liquids, and additional sealing or frictional features) or methods may be used to achieve increased torque retention or removal torques in excess of an applied set torque.

In an exemplary method of assembly of the apparatus, fitment 6 is snap-fitted to container 4 and mating threads 20 and 22 are then engaged by rotation of closure 8 relative to container 4. Continued rotational engagement and axial advancement brings various projections and recesses into sealing engagement as described above. Finally, application of a set torque as shown in FIGS. 2-3 generates residual forces including compression of and friction between mating threads 20-22. Alternatively, fitment 6 may be attached first to closure 8, with the combination then being attached to container 4 by engagement of any suitable complimentary features. Thus, closure 6 may be retained by container 4 or may be retained by fitment 6 which may in turn be retained by container 4. Any sequence or method of assembly or attachment of container 4, fitment 6, and/or closure 8 may be suitably employed in accordance with the present invention.

Tests were conducted with various container-fitment-closure assemblies 2 according to the present invention. Test containers 4 were injection molded from polypropylene, wick fitments 6 of linear low density polyethylene, and closures 8 of polypropylene. 120 test assemblies 2 were configured essentially as shown in FIG. 2 and described above. Containers 4 were filled with scented oil. Wick fitments 6, with wicks mounted therein, were then snap-fitted to test containers 4. Closures 8 were then threadably assembled to containers 4 with set torques of between 3 and 10 inch pounds per set. Test assemblies 2 were then heated to 120° F., vacuum tested to 12,000 ft. and placed back in the 120° F. oven for period of between twenty-four hours and one week to simulate the effects of creep and aging associated with the expected storage life.

Closures 8 were then removed and the removal torque values were recorded as shown in Table 1. These results are summarized in Table 1 below. TABLE 1 Test Torque Period 3-lbs 4-lbs 5-lbs 6-lbs 7-lbs 8-lbs 9-lbs 10-lbs 24-Hours 7.7 4.9 5.1 6.0 7.1 7.0 6.7 9.3 24-Hours 5.7 6.5 5.1 7.2 8.3 7.3 9.4 7.7 24-Hours 4.3 4.1 5.2 6.2 6.7 7.2 7.7 6.6 24-Hours 5.3 4.5 5.6 6.8 7.8 7.2 6.2 7.8 24-Hours 6.1 6.5 4.6 5.5 7.7 7.4 6.6 9.5 Average = 5.82 5.30 5.12 6.34 7.52 7.22 7.32 8.18 144-Hours 4.7 6.0 7.0 6.4 6.7 6.6 6.1 6.7 144-Hours 6.5 5.6 6.4 6.6 5.5 7.6 4.4 8.5 144-Hours 6.5 6.5 5.8 6.5 6.2 5.6 7.0 7.8 144-Hours 7.6 8.4 4.7 5.9 6.2 5.5 7.0 7.8 144-Hours 5.0 5.7 6.0 5.5 6.0 6.5 8.2 6.4 Average = 6.06 6.44 5.98 6.18 6.12 6.36 6.40 7.96 1-Week 5.8 6.3 6.1 6.0 5.5 5.8 7.0 8.7 1-Week 6.2 6.0 6.6 7.8 6.6 6.9 9.5 6.6 1-Week 6.1 7.8 8.5 6.3 7.2 7.6 7.3 7.5 1-Week 6.5 6.5 6.2 6.3 9.5 6.3 7.7 9.0 1-Week 7.0 9.0 5.6 7.2 6.9 8.2 8.5 6.4 Average = 6.32 7.12 6.60 6.72 7.14 6.96 8.00 7.64

As can be seen from Table 1, at the conclusion of the tests, it was found that the present invention provides torque retention of substantially greater than fifty percent. The removal torque does not linearly correspond with the set torque. For example, a set torque of between 8 and 10 inch pounds resulted in torque retentions in excess of seventy-five percent while a set torque of between 3 and 7 inch pounds resulted in removal torques well in excess of the applied set torque, or, in other words, exhibiting torque retention of greater than one-hundred percent.

For the sake of brevity, conventional mechanical and industrial design techniques used in developing various devices (and the various components thereof) are not described in detail herein. Accordingly, devices disclosed herein may be readily modified to create equivalent embodiments through application of general mechanical, industrial and/or manufacturing principles. The particular implementations shown and described herein are examples of the invention and are not intended to otherwise limit the scope of the invention in any way. In this context, the corresponding structures, materials, acts and equivalents of all elements described herein, are intended to include any structure, material or acts for performing the functions described herein and include those now known or hereafter devised. 

1. A torque retention apparatus for use with a container and closure combination, the apparatus comprising: a first retainer formed on the container, said first retainer comprised of a first polymer; a second retainer formed on the closure and configured to engage said first retainer through application of a set torque during installation of the closure on the container, said second retainer comprised of a second polymer, said first and second polymers selected such that a removal torque applied to disengage said first and second retainers following an extended period of engagement is substantially greater than fifty percent of said set torque.
 2. The apparatus of claim 1, wherein said removal torque is at least equal to said set torque.
 3. The apparatus of claim 1, wherein said first and second polymers are selected from the group consisting of polypropylene, polyethylene, polyvinyl chloride, and copolymers of the same.
 4. The apparatus of claim 1, wherein said first and second retainers comprise complimentary threads.
 5. The apparatus of claim 1, wherein a substance contained by the container is selected to interact with at least one of said first and second polymers to contribute to said removal torque.
 6. The apparatus of claim 1, further comprising a fitment interposed between the container and the closure, said fitment configured to attach to at least one of the container and the closure, said fitment at least one of configured to and comprised of a material selected to contribute to said removal torque.
 7. The apparatus of claim 6, wherein said fitment is a wick holder comprising: a tubular portion for receiving a wick; at least a first sealing feature for sealingly engaging the closure; and at least a second sealing feature for sealingly engaging the container.
 8. The apparatus of claim 7, wherein at least one of said first and second sealing features contributes to said removal torque.
 9. The apparatus of claim 8, wherein relative material properties of said first and second polymers, interaction between container contents and at least one of said first polymer, said second polymer and said fitment, and friction generated by at least one of said first and second sealing features cooperate to contribute to said removal torque.
 10. The apparatus of claim 7, wherein said fitment includes at least one of a circumferential skirt for engaging the neck of the container and an annular well surrounding said tubular portion.
 11. The apparatus of claim 10, wherein said first sealing feature is an annular projection contacting an outer sidewall of said well, and said second sealing feature is an annular projection on the closure contacting a complimentary annular grove in a top surface of said fitment.
 12. The apparatus of claim 1, wherein a first said removal torque is between 100 percent and 250 percent of a first said set torque, a second said removal torque is between 100 percent and 150 percent of a second said set torque of twice said first said set torque, and a third said removal torque is between 75 percent and 100 percent of a third said set torque of three times said first said set torque.
 13. A torque retention apparatus for use with a container and closure combination, the apparatus comprising: a fitment interposed between the container and the closure and attachable to at least one of the container and the closure; a first retainer formed on one of the container and said fitment, said first retainer comprised of a first polymer; a second retainer formed on one of the closure and said fitment and configured to engage said first retainer through application of a set torque during installation of one of the closure and said fitment on the container, said second retainer comprised of a second polymer, said first and second polymers selected such that a removal torque applied to disengage said first and second retainers following an extended period of engagement is substantially greater than fifty percent of said set torque.
 14. The apparatus of claim 13, wherein the closure is retained by at least one of the container and said fitment.
 15. The apparatus of claim 13, further comprising a friction generating feature in addition to said first and second retainers contributing to said removal torque.
 16. The apparatus of claim 13, wherein at least two of a sealing feature formed on one of the container, the closure, and said fitment, a frictional feature formed on one of the container, the closure, and said fitment, and a substance contained in the container contribute to said removal torque.
 17. An improved container-closure combination, the improvement comprising: a first retainer of a first polymer formed on the container; a second retainer of a second polymer formed on the closure for rotational engagement of said first retainer by application of a set torque, said first and second polymers selected such that a removal torque required to disengage said first and second retainers following an extended period of engagement is substantially greater than fifty percent of said set torque.
 18. A method of increasing torque retention in rotationally engaged combinations, the method comprising: selecting a first polymer; forming a first retainer on a first component, said first retainer comprised of said first polymer; selecting a second polymer; forming a second retainer from said second polymer on a second component for rotational engagement with said first retainer, and applying a set torque between said first and second components to engage said first and second retainers with frictional interference between said first and second retainers, a relative difference in a material property of said first and second polymers contributing to a reduced degree of loss of the frictional interference over time such that a removal torque required to overcome the frictional interference following at least one of an extended period of engagement at ambient temperature and a shortened period of engagement at an elevated temperature is substantially greater than fifty percent of said set torque.
 19. The method of claim 18, wherein at least one of said forming steps comprises forming at least one of said first and second retainers from at least one of polypropylene, and polyethylene.
 20. The method of claim 18, further comprising selecting a liquid for interaction with at least one of said first and second polymers to further reduce said degree of loss of said frictional interference.
 21. The method of claim 18, wherein said first forming step comprises forming threads on a container, said second forming step comprises forming complimentary threads on a closure, the method further comprising forming a fitment configured to attach to at least one of the container and the closure from at least one of said first polymer, said second polymer, and a third polymer.
 22. The method of claim 18, wherein said steps of selecting said first and second polymers contribute to said removal torque being in excess of said set torque. 